1. Field of the Invention
This invention relates to the preparation of sulfonyl peroxides. More particularly, it relates to the preparation of sulfonyl peroxides such as acetyl cyclohexanesulfonyl peroxide by reaction of SO.sub.2 and O.sub.2 with an alkane or cycloalkane reactant and acylation with a carboxylic acid anhydride.
2. Description of the Prior Art
The basic process for the preparation of sulfonyl peroxides by sulfoxidation of saturated hydrocarbons and subsequent acylation with carboxylic acid anhydrides is shown in two references: L. Orthner, Angew. Chem., 62 302-5 (1950) and R. Graf, Ann. Chem., 578, 50-82 (1952). U.S. Pat. No. 3,586,722 to Sanchez (1971) describes the preparation of certain sulfonyl peroxides by the method of Graf and Orthner.
German Pat. No. 840,093 (1952) reports the preparation of alkanesulfonic acids by sulfoxidation of a saturated, non-aromatic hydrocarbon such as propane, n-butane, 3-methylheptane, cyclohexane, and methylcyclohexane and continuous extraction of product from the reaction mixture. Extraction may be performed in the sulfoxidation reactor or in an external extraction column. Suitable extraction solvents are immiscible with the hydrocarbon and include water, liquid sulfur dioxide, alcohols, low molecular weight fatty acids, acetonitrile, acetic anhydride, and mixtures of solvents as mixtures of methanol and water.
When sulfonyl peroxides are prepared by the method of Graf and Orthner, the product usually separates as a crude oily layer beneath the hydrocarbon reaction phase in the reactor. Both the crude oily products and the pure peroxides present a danger of violent decomposition or explosion and, although the crude oils are less dangerous than the pure peroxides, strong safety precautions such as heavy shielding, bunkers, and remote control of equipment should be employed in constructing a reactor.
The Sanchez patent shows the preparation of sulfonyl peroxides in a single liquid phase having a saturated hydrocarbon dissolved in a polar solvent which is inert to sulfoxidation, such as methylene chloride. The peroxide is obtained in solution in the polar solvent, and is then isolated by vacuum stripping.
Sulfonyl peroxides are much less dangerous when in solution, and solutions in certain solvents have commercial utility. For example, acetyl cyclohexanesulfonyl peroxide is a widely used polymerization initiator. When dry, it forms crystals which can detonate on minor impact. It is commonly sold dissolved in dimethyl phthalate, typically in concentrations of about 10 to about 35 weight percent, because the presence of small amounts of phthalate ester in finished polymers is often acceptable, whereas the presence of another solvent, methylene chloride for example, would not be acceptable.
The German patent recognizes that the sulfoxidation reaction may be carried out in the presence of an immiscible solvent. However, Graf, Orthner, and Sanchez all state that olefins and aromatic hydrocarbons, e.g., benzene, are inhibitors of the sulfoxidation reaction. Accordingly, no report has been found describing preparation of sulfonyl peroxides by sulfoxidation of saturated hydrocarbons and acylation with carboxylic acid anhydrides in the presence of aromatic solvents.